Medical Imaging devices that provide both morphological and molecular-functional information in one imaging session have gained acceptance as the diagnostic imaging tools of choice, because of the substantial increase in benefit for patients and physicians. Currently, almost all positron emission tomography (PET) systems sold have an integrated computed tomography (CT) scanner. In spite of the good performance of PET-CT systems, such devices are limited by (a) the low soft-tissue contrast of CT, and (b) the lack of simultaneous PET-CT image acquisition prohibiting the correction of organ/patient motion artifacts and the misregistration in the fused images. Therefore to overcome these handicaps, a novel approach is to integrate PET with a magnetic resonance (MR) system [23].
The integration of PET and MR has several advantages, including: (a) superior and flexible contrast for soft tissue, improving cancer diagnosis such as prostate imaging; (b) since 4D (x, y, z, t) MRI imaging can be acquired simultaneously with PET acquisition, PET-MR will have accurate image fusion, correction for motion artifacts, misregistration and 4D attenuation correction; (c) the much higher resolution of MR can be used for correcting the partial-volume effect of the lower resolution PET images to provide more accurate PET quantitation and diagnosis; (d) MR does not impart radiation dose to patients as CT scans that has caused concern in recent years; (e) one can study the correlation of functional MRI studies and PET blood-flow measurements; (f) PET metabolic studies and MR protein spectroscopy can be synergized in the study of metabolism.
However, since MR images show proton density and tissue-relaxation properties and not electron density and mass density, the PET attenuation correction using MR is more complicated than CT.
Despite MR-PET's enormous potential, its high cost is a major barrier preventing the wide availability of MR-PET. A whole-body PET-MR without time-of-flight capability cost $5 million, which is much more than that of the combined stand-alone 3T MR and a stand-along PET ($3.5 million). Furthermore, despite the high-cost technology, current whole-body MR-PET from Siemens, a leader in MR-PET technology, has an intrinsic PET resolution of 4.3-mm that is no better than the resolution of the Siemens PET-CT for the last two decades.
Proposed herein is a new MR-PET detector design that can reduce the costly MR-PET detector system substantially and provides superior PET imaging resolution to the current MR-PET systems. This novel design has another important feature that it is scalable (stretchable) so the design can achieve resolution from 1-mm for preclinical imaging to 2.5 mm (or better) for human imaging, improving the current 4-5 mm human MR-PET resolution.
In addition, with the scalable-detector characteristics, its detector-processing electronics do not change with the detector-array dimensions or detector-pixel sizes, unlike current PET-MR using fixed SiPM panels. Hence, the same detector-readout electronics made for one detector type (e.g., mouse MR-PET) can also be used for the large human MR-PET, thereby minimizing the effort/cost of electronic development for different MR-PET systems.
Hence, embodiments disclosed herein could yield one comprehensive detector-platform technology that yields ultrahigh-resolution detectors and electronics from preclinical MR-PET, to whole-body MR-PET, to organ-specific MR-PET such as breast MR-PET and brain MR-PET. The novel elasticity of the proposed detector design can be demonstrated by implementing MR-PET detectors for different imaging applications and resolutions.
In addition, this low-cost and flexible MR-PET detector technology can create low-cost depth-of-interaction-localizing (DOI) detectors to improve the off-center image blurring from DOI effect that is well known but has not been solved cost-effectively. The latest clinical MR-PET and PET-CT systems still do not have the DOI capability after more than 30 years of research in DOI detectors. The enabling of low-cost DOI PET detector with the proposed design is significant for realizing ultrahigh resolution MR-PET, because the MR bore is small, about 70 cm, and the entire PET detector ring and front-end electronics has to be inside this 70 cm diameter. Hence the Siemens whole-body MR-PET detector ring has to be reduced to a small 65-cm, much smaller than the PET-CT's 85-cm detector-diameter ring. But with the regular patient bore (FOV) maintaining at 60-cm, the 65-cm detector ring is almost touching the patient, thus making the DOI blurring effect more severe in MR-PET, especially if PET resolution (detector-pixel size) is improved to 2-2.5 mm using our detector design. With the proposed technology, a lower-cost, practical MR-PET with DOI-localization can be realized to solve this severe problem in MR-PET. It is expected the median resolution of 5.5-mm within a 40 cm FOV in current MR-PET can be reduced to 2-2.5 mm.